topic Re: Need a joint that removes one degree of freedom in Fusion Support Forum

Need a joint that removes one degree of freedom

Frommologistad — Wed, 24 Jan 2024 02:21:01 GMT

I often want to remove one degree of freedom of a component, but there is not a joint that does that. For example: a bracket with a hole and a slot is mounted to a plate with two holes. A revolute joint can be added to mate the bracket hole to the plate hole. But there is no joint that will remove the single remaining degree of freedom of the bracket rotating around the hole. There needs to be a way to locate one component relative to two features of another component. The work around is use a Rigid joint and eyeball the angle setting until the hole looks to be aligned with the slot. If you move the slot you have to find the Rigid joint and adjust the angle again.

The Planner joint removes 2 degrees for freedom: a point on a plane and an axis normal to the plane. The axis required to be normal is the problem.
Using Inventor the constraints acted differently (as to how many degrees of freedom were removed) depending on the elements (plane, line or point) selected as input. Not so with Fusion 360.

Re: Need a joint that removes one degree of freedom

g-andresen — Tue, 23 Jan 2024 15:52:38 GMT

Hi,

A cylindrical joint might be able to help.

But:
Without an insight into the file, one can only speculate.
Please share the file

File > export > save as f3d on local drive > attach to post

günther

Re: Need a joint that removes one degree of freedom

jhackney1972 — Tue, 23 Jan 2024 22:36:21 GMT

You say you add a Revolve Joint and then have no option except line up the second hole using your eye. Did you ever consider using another Revolve joint on the second hole to line it up. Not only does this do the job precisely but it checks you hole spacing. Take a look at the Animated GIF.

Edit: changed Joint type to handle all orientations

Re: Need a joint that removes one degree of freedom

Frommologistad — Wed, 24 Jan 2024 02:37:02 GMT

Thank you for the responses. Yes, If there are 2 holes at have exactly the same spacing a cylindrical joint has worked, I am surprised a rigid joint works too. Neither of these "should" work since more than 6 degrees of freedom have been removed. If the hole spacing is not precisely the same, and their axes parallel, neither method will work.
I have edited my post and added two files. (I am new to this communication method and not sure of best methods.) One file is the simple example I described... I want to constrain Component1 slot to Body1 hole such that when the holes in Body1 move the slot in Component1 will still be over the hole in Body1.

The other file is the real case. "Plate 1 Motor" is rotating around "Falcon V3 Simple". "Falcon V3" is jointed to sketch "All Centers" via a component or two. Unlock joint "Hex to Falcon" and the plate will spin, I want the hex shaft "1_2 Hex x 0.159ID ThunderHex" to touch the "Frame Rail; 1" or the edge of the plate to be horizontal or vertical.
Thanks for your thoughts. Paul

Re: Need a joint that removes one degree of freedom

davebYYPCU — Wed, 24 Jan 2024 11:25:02 GMT

As I read it, you want the bottom flat face of the hex to align with the top of the horizontal bar.

That hex is assembled in the rotating plate correctly but has all round clearance.

To make the rotating plate align, (less that 1 degree off - would align both)

you either adjust the rotation angle in the rest position or joint offset dialogue box.

Then the plate would have to drop by the clearance amount.

Might help...

Will check back tomorrow.

Re: Need a joint that removes one degree of freedom

Frommologistad — Wed, 24 Jan 2024 23:22:31 GMT

Thank you for your response. I agree that joint can be adjusted laboriously to achieve alignment for the current state of the model. If I move other parts of the model it is likely I will have to re-adjust a joint to get parts in the correct position again.
The point of my post is that Fusion 360 developers should add a joint that removes only one degree of freedom, such as a point on a plane. If there was such a joint, components would remain in the design intent alignment as features within a component are adjusted. My simple two component example files with a plate with 2 holes and a plate with one hole and a slot is not constrainable in a way that captures the design intent with the set of joint Fusion 360 has. Mounting parts with a hole and a slot is extremely common.

Re: Need a joint that removes one degree of freedom

Frommologistad — Wed, 24 Jan 2024 23:24:31 GMT

Thank you. I have added some files to the original post. I think I replied to myself so you may not have noticed.

Re: Need a joint that removes one degree of freedom

Frommologistad — Wed, 24 Jan 2024 23:26:38 GMT

Thank you. I think I replied to myself so you may not have noticed.

Re: Need a joint that removes one degree of freedom

davebYYPCU — Thu, 25 Jan 2024 02:39:05 GMT

is not constrainable in a way that captures the design intent

What design intent are you after?

Simple enough.

Re: Need a joint that removes one degree of freedom

Frommologistad — Thu, 25 Jan 2024 22:24:15 GMT

Agree. We need a new joint. The design intent is to have the slot remain aligned to the second hole, even when I move the second hole. Like editing the 0.7" to 1".

Re: Need a joint that removes one degree of freedom

davebYYPCU — Fri, 26 Jan 2024 00:46:08 GMT

Changing the hole dia, has no effect on the slot, unless you move the hole, but still a simple job.

Even that can be done with preparation.

Might help....

Re: Need a joint that removes one degree of freedom

Frommologistad — Tue, 30 Jan 2024 02:08:03 GMT

Agree the hole diameter has no effect on the rev or rigid joints.

Disagree with preparation can be done to make the slot in one part follow the hole in the other part. I imagine that the rigid joint might stay aligned to the origin of the part with the 2 holes... so if the hole stayed fixed relative the origin of the part with two holes and the rest of the part move relative to the hole and origin, then the part with the slot would remain aligned to the hole. This is plausible but not practical. It is easy to image a plurality of parts with slots that need to follow holes in a mating part. Also constraining a part shape & sketches to rotate around the origin relative to some hole seems arduous. Did you have some other "preparation" in mind?

Re: Need a joint that removes one degree of freedom

davebYYPCU — Tue, 30 Jan 2024 04:27:40 GMT

Disagree (-) with preparation can be done to make the slot in one part follow the hole in the other part.

Change d5 to something else.

Might help...

Re: Need a joint that removes one degree of freedom

Frommologistad — Thu, 08 Feb 2024 02:43:30 GMT

Thank you for your suggestion, but constrain 2 shapes within a sketch is not equivalent to constraining one component to another component. If one sketch shape is extruded to a new component and the other shape extruded to a second component the locational relationship in the sketch is lost.

I still think Fusion 360 is missing a needed joint that will remove 1 degree of freedom.